Thread: Removing a constraint?

Does anyone know how to completely and accurately remove or drop a
constraint, specifically a foreign key constraint?  I tried to remove a
constraint by deleting it's trigger from pg_triggers.  This caused some
undesirable side effects with other tables involved with the constraint.  I
have several tables that I need to change the column constraints and
foreign key constraints on.  Recreating (drop and create) the table every
time I need to change a column constraint is a pain because all the objects
that reference the table would also need to be recreated (i.e. views and
triggers).  How do production DBAs successfully make changes to their
tables?

FYI, I was able to alter table add the same constraint many times.  Is this
a problem?  This created a new trigger in pg_triggers every time.

It should work if you remove all three triggers for the constraint
using drop trigger, don't delete rows from pg_trigger unless you go
through and manually change the row in pg_class for the relation
the trigger is for.

On Mon, 1 Jan 2001, Michael Davis wrote:

> Does anyone know how to completely and accurately remove or drop a
> constraint, specifically a foreign key constraint?  I tried to remove a
> constraint by deleting it's trigger from pg_triggers.  This caused some
> undesirable side effects with other tables involved with the constraint.  I
> have several tables that I need to change the column constraints and
> foreign key constraints on.  Recreating (drop and create) the table every
> time I need to change a column constraint is a pain because all the objects
> that reference the table would also need to be recreated (i.e. views and
> triggers).  How do production DBAs successfully make changes to their
> tables?
>
> FYI, I was able to alter table add the same constraint many times.  Is this
> a problem?  This created a new trigger in pg_triggers every time.

Michael Davis wrote:

> Does anyone know how to completely and accurately remove or drop a
> constraint, specifically a foreign key constraint?  I tried to remove a
> constraint by deleting it's trigger from pg_triggers.  This caused some
> undesirable side effects with other tables involved with the constraint.  I
> have several tables that I need to change the column constraints and
> foreign key constraints on.  Recreating (drop and create) the table every
> time I need to change a column constraint is a pain because all the objects
> that reference the table would also need to be recreated (i.e. views and
> triggers).  How do production DBAs successfully make changes to their
> tables?
>
> FYI, I was able to alter table add the same constraint many times.  Is this
> a problem?  This created a new trigger in pg_triggers every time.

A bug in "cluster" will do this, if you cluster a table it will drop all
constraints and indexes.

One could use pg_dump, as:

pg_dump -a -t table database > table_data.sql
pg_dump -s -t table database >  table_schema.sql

(edit table_schema.sql to remove constraint)

psql database < table_schema.sql
psql database < table_data.sql